| FastBoot Version 0.4 | |
| ---------------------- | |
| The fastboot protocol is a mechanism for communicating with bootloaders | |
| over USB or ethernet. It is designed to be very straightforward to implement, | |
| to allow it to be used across a wide range of devices and from hosts running | |
| Linux, Windows, or OSX. | |
| Basic Requirements | |
| ------------------ | |
| * USB | |
| * Two bulk endpoints (in, out) are required | |
| * Max packet size must be 64 bytes for full-speed, 512 bytes for | |
| high-speed and 1024 bytes for Super Speed USB. | |
| * The protocol is entirely host-driven and synchronous (unlike the | |
| multi-channel, bi-directional, asynchronous ADB protocol) | |
| * TCP or UDP | |
| * Device must be reachable via IP. | |
| * Device will act as the server, fastboot will be the client. | |
| * Fastboot data is wrapped in a simple protocol; see below for details. | |
| Transport and Framing | |
| --------------------- | |
| 1. Host sends a command, which is an ascii string in a single | |
| packet no greater than 64 bytes. | |
| 2. Client response with a single packet no greater than 64 bytes. | |
| The first four bytes of the response are "OKAY", "FAIL", "DATA", | |
| or "INFO". Additional bytes may contain an (ascii) informative | |
| message. | |
| a. INFO -> the remaining 60 bytes are an informative message | |
| (providing progress or diagnostic messages). They should | |
| be displayed and then step #2 repeats | |
| b. FAIL -> the requested command failed. The remaining 60 bytes | |
| of the response (if present) provide a textual failure message | |
| to present to the user. Stop. | |
| c. OKAY -> the requested command completed successfully. Go to #5 | |
| d. DATA -> the requested command is ready for the data phase. | |
| A DATA response packet will be 12 bytes long, in the form of | |
| DATA00000000 where the 8 digit hexadecimal number represents | |
| the total data size to transfer. | |
| 3. Data phase. Depending on the command, the host or client will | |
| send the indicated amount of data. Short packets are always | |
| acceptable and zero-length packets are ignored. This phase continues | |
| until the client has sent or received the number of bytes indicated | |
| in the "DATA" response above. | |
| 4. Client responds with a single packet no greater than 64 bytes. | |
| The first four bytes of the response are "OKAY", "FAIL", or "INFO". | |
| Similar to #2: | |
| a. INFO -> display the remaining 60 bytes and return to #4 | |
| b. FAIL -> display the remaining 60 bytes (if present) as a failure | |
| reason and consider the command failed. Stop. | |
| c. OKAY -> success. Go to #5 | |
| 5. Success. Stop. | |
| Example Session | |
| --------------- | |
| Host: "getvar:version" request version variable | |
| Client: "OKAY0.4" return version "0.4" | |
| Host: "getvar:nonexistant" request some undefined variable | |
| Client: "OKAY" return value "" | |
| Host: "download:00001234" request to send 0x1234 bytes of data | |
| Client: "DATA00001234" ready to accept data | |
| Host: < 0x1234 bytes > send data | |
| Client: "OKAY" success | |
| Host: "flash:bootloader" request to flash the data to the bootloader | |
| Client: "INFOerasing flash" indicate status / progress | |
| "INFOwriting flash" | |
| "OKAY" indicate success | |
| Host: "powerdown" send a command | |
| Client: "FAILunknown command" indicate failure | |
| Command Reference | |
| ----------------- | |
| * Command parameters are indicated by printf-style escape sequences. | |
| * Commands are ascii strings and sent without the quotes (which are | |
| for illustration only here) and without a trailing 0 byte. | |
| * Commands that begin with a lowercase letter are reserved for this | |
| specification. OEM-specific commands should not begin with a | |
| lowercase letter, to prevent incompatibilities with future specs. | |
| "getvar:%s" Read a config/version variable from the bootloader. | |
| The variable contents will be returned after the | |
| OKAY response. | |
| "download:%08x" Write data to memory which will be later used | |
| by "boot", "ramdisk", "flash", etc. The client | |
| will reply with "DATA%08x" if it has enough | |
| space in RAM or "FAIL" if not. The size of | |
| the download is remembered. | |
| "verify:%08x" Send a digital signature to verify the downloaded | |
| data. Required if the bootloader is "secure" | |
| otherwise "flash" and "boot" will be ignored. | |
| "flash:%s" Write the previously downloaded image to the | |
| named partition (if possible). | |
| "erase:%s" Erase the indicated partition (clear to 0xFFs) | |
| "boot" The previously downloaded data is a boot.img | |
| and should be booted according to the normal | |
| procedure for a boot.img | |
| "continue" Continue booting as normal (if possible) | |
| "reboot" Reboot the device. | |
| "reboot-bootloader" Reboot back into the bootloader. | |
| Useful for upgrade processes that require upgrading | |
| the bootloader and then upgrading other partitions | |
| using the new bootloader. | |
| "powerdown" Power off the device. | |
| Client Variables | |
| ---------------- | |
| The "getvar:%s" command is used to read client variables which | |
| represent various information about the device and the software | |
| on it. | |
| The various currently defined names are: | |
| version Version of FastBoot protocol supported. | |
| It should be "0.4" for this document. | |
| version-bootloader Version string for the Bootloader. | |
| version-baseband Version string of the Baseband Software | |
| product Name of the product | |
| serialno Product serial number | |
| secure If the value is "yes", this is a secure | |
| bootloader requiring a signature before | |
| it will install or boot images. | |
| Names starting with a lowercase character are reserved by this | |
| specification. OEM-specific names should not start with lowercase | |
| characters. | |
| TCP Protocol v1 | |
| --------------- | |
| The TCP protocol is designed to be a simple way to use the fastboot protocol | |
| over ethernet if USB is not available. | |
| The device will open a TCP server on port 5554 and wait for a fastboot client | |
| to connect. | |
| -- Handshake -- | |
| Upon connecting, both sides will send a 4-byte handshake message to ensure they | |
| are speaking the same protocol. This consists of the ASCII characters "FB" | |
| followed by a 2-digit base-10 ASCII version number. For example, the version 1 | |
| handshake message will be [FB01]. | |
| If either side detects a malformed handshake, it should disconnect. | |
| The protocol version to use must be the minimum of the versions sent by each | |
| side; if either side cannot speak this protocol version, it should disconnect. | |
| -- Fastboot Data -- | |
| Once the handshake is complete, fastboot data will be sent as follows: | |
| [data_size][data] | |
| Where data_size is an unsigned 8-byte big-endian binary value, and data is the | |
| fastboot packet. The 8-byte length is intended to provide future-proofing even | |
| though currently fastboot packets have a 4-byte maximum length. | |
| -- Example -- | |
| In this example the fastboot host queries the device for two variables, | |
| "version" and "none". | |
| Host <connect to the device on port 5555> | |
| Host FB01 | |
| Device FB01 | |
| Host [0x00][0x00][0x00][0x00][0x00][0x00][0x00][0x0E]getvar:version | |
| Device [0x00][0x00][0x00][0x00][0x00][0x00][0x00][0x07]OKAY0.4 | |
| Host [0x00][0x00][0x00][0x00][0x00][0x00][0x00][0x0B]getvar:none | |
| Device [0x00][0x00][0x00][0x00][0x00][0x00][0x00][0x04]OKAY | |
| Host <disconnect> | |
| UDP Protocol v1 | |
| --------------- | |
| The UDP protocol is more complex than TCP since we must implement reliability | |
| to ensure no packets are lost, but the general concept of wrapping the fastboot | |
| protocol is the same. | |
| Overview: | |
| 1. As with TCP, the device will listen on UDP port 5554. | |
| 2. Maximum UDP packet size is negotiated during initialization. | |
| 3. The host drives all communication; the device may only send a packet as a | |
| response to a host packet. | |
| 4. If the host does not receive a response in 500ms it will re-transmit. | |
| -- UDP Packet format -- | |
| +----------+----+-------+-------+--------------------+ | |
| | Byte # | 0 | 1 | 2 - 3 | 4+ | | |
| +----------+----+-------+-------+--------------------+ | |
| | Contents | ID | Flags | Seq # | Data | | |
| +----------+----+-------+-------+--------------------+ | |
| ID Packet ID: | |
| 0x00: Error. | |
| 0x01: Query. | |
| 0x02: Initialization. | |
| 0x03: Fastboot. | |
| Packet types are described in more detail below. | |
| Flags Packet flags: 0 0 0 0 0 0 0 C | |
| C=1 indicates a continuation packet; the data is too large and will | |
| continue in the next packet. | |
| Remaining bits are reserved for future use and must be set to 0. | |
| Seq # 2-byte packet sequence number (big-endian). The host will increment | |
| this by 1 with each new packet, and the device must provide the | |
| corresponding sequence number in the response packets. | |
| Data Packet data, not present in all packets. | |
| -- Packet Types -- | |
| Query The host sends a query packet once on startup to sync with the device. | |
| The host will not know the current sequence number, so the device must | |
| respond to all query packets regardless of sequence number. | |
| The response data field should contain a 2-byte big-endian value | |
| giving the next expected sequence number. | |
| Init The host sends an init packet once the query response is returned. The | |
| device must abort any in-progress operation and prepare for a new | |
| fastboot session. This message is meant to allow recovery if a | |
| previous session failed, e.g. due to network error or user Ctrl+C. | |
| The data field contains two big-endian 2-byte values, a protocol | |
| version and the max UDP packet size (including the 4-byte header). | |
| Both the host and device will send these values, and in each case | |
| the minimum of the sent values must be used. | |
| Fastboot These packets wrap the fastboot protocol. To write, the host will | |
| send a packet with fastboot data, and the device will reply with an | |
| empty packet as an ACK. To read, the host will send an empty packet, | |
| and the device will reply with fastboot data. The device may not give | |
| any data in the ACK packet. | |
| Error The device may respond to any packet with an error packet to indicate | |
| a UDP protocol error. The data field should contain an ASCII string | |
| describing the error. This is the only case where a device is allowed | |
| to return a packet ID other than the one sent by the host. | |
| -- Packet Size -- | |
| The maximum packet size is negotiated by the host and device in the Init packet. | |
| Devices must support at least 512-byte packets, but packet size has a direct | |
| correlation with download speed, so devices are strongly suggested to support at | |
| least 1024-byte packets. On a local network with 0.5ms round-trip time this will | |
| provide transfer rates of ~2MB/s. Over WiFi it will likely be significantly | |
| less. | |
| Query and Initialization packets, which are sent before size negotiation is | |
| complete, must always be 512 bytes or less. | |
| -- Packet Re-Transmission -- | |
| The host will re-transmit any packet that does not receive a response. The | |
| requirement of exactly one device response packet per host packet is how we | |
| achieve reliability and in-order delivery of packets. | |
| For simplicity of implementation, there is no windowing of multiple | |
| unacknowledged packets in this version of the protocol. The host will continue | |
| to send the same packet until a response is received. Windowing functionality | |
| may be implemented in future versions if necessary to increase performance. | |
| The first Query packet will only be attempted a small number of times, but | |
| subsequent packets will attempt to retransmit for at least 1 minute before | |
| giving up. This means a device may safely ignore host UDP packets for up to 1 | |
| minute during long operations, e.g. writing to flash. | |
| -- Continuation Packets -- | |
| Any packet may set the continuation flag to indicate that the data is | |
| incomplete. Large data such as downloading an image may require many | |
| continuation packets. The receiver should respond to a continuation packet with | |
| an empty packet to acknowledge receipt. See examples below. | |
| -- Summary -- | |
| The host starts with a Query packet, then an Initialization packet, after | |
| which only Fastboot packets are sent. Fastboot packets may contain data from | |
| the host for writes, or from the device for reads, but not both. | |
| Given a next expected sequence number S and a received packet P, the device | |
| behavior should be: | |
| if P is a Query packet: | |
| * respond with a Query packet with S in the data field | |
| else if P has sequence == S: | |
| * process P and take any required action | |
| * create a response packet R with the same ID and sequence as P, containing | |
| any response data required. | |
| * transmit R and save it in case of re-transmission | |
| * increment S | |
| else if P has sequence == S - 1: | |
| * re-transmit the saved response packet R from above | |
| else: | |
| * ignore the packet | |
| -- Examples -- | |
| In the examples below, S indicates the starting client sequence number. | |
| Host Client | |
| ====================================================================== | |
| [Initialization, S = 0x55AA] | |
| [Host: version 1, 2048-byte packets. Client: version 2, 1024-byte packets.] | |
| [Resulting values to use: version = 1, max packet size = 1024] | |
| ID Flag SeqH SeqL Data ID Flag SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x01 0x00 0x00 0x00 | |
| 0x01 0x00 0x00 0x00 0x55 0xAA | |
| 0x02 0x00 0x55 0xAA 0x00 0x01 0x08 0x00 | |
| 0x02 0x00 0x55 0xAA 0x00 0x02 0x04 0x00 | |
| ---------------------------------------------------------------------- | |
| [fastboot "getvar" commands, S = 0x0001] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0x00 0x01 getvar:version | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x00 0x00 0x02 | |
| 0x03 0x00 0x00 0x02 OKAY0.4 | |
| 0x03 0x00 0x00 0x03 getvar:foo | |
| 0x03 0x00 0x00 0x03 | |
| 0x03 0x00 0x00 0x04 | |
| 0x03 0x00 0x00 0x04 OKAY | |
| ---------------------------------------------------------------------- | |
| [fastboot "INFO" responses, S = 0x0000] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0x00 0x00 <command> | |
| 0x03 0x00 0x00 0x00 | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x00 0x00 0x01 INFOWait1 | |
| 0x03 0x00 0x00 0x02 | |
| 0x03 0x00 0x00 0x02 INFOWait2 | |
| 0x03 0x00 0x00 0x03 | |
| 0x03 0x00 0x00 0x03 OKAY | |
| ---------------------------------------------------------------------- | |
| [Chunking 2100 bytes of data, max packet size = 1024, S = 0xFFFF] | |
| ID Flag SeqH SeqL Data ID Flag SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0xFF 0xFF download:0000834 | |
| 0x03 0x00 0xFF 0xFF | |
| 0x03 0x00 0x00 0x00 | |
| 0x03 0x00 0x00 0x00 DATA0000834 | |
| 0x03 0x01 0x00 0x01 <1020 bytes> | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x01 0x00 0x02 <1020 bytes> | |
| 0x03 0x00 0x00 0x02 | |
| 0x03 0x00 0x00 0x03 <60 bytes> | |
| 0x03 0x00 0x00 0x03 | |
| 0x03 0x00 0x00 0x04 | |
| 0x03 0x00 0x00 0x04 OKAY | |
| ---------------------------------------------------------------------- | |
| [Unknown ID error, S = 0x0000] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x10 0x00 0x00 0x00 | |
| 0x00 0x00 0x00 0x00 <error message> | |
| ---------------------------------------------------------------------- | |
| [Host packet loss and retransmission, S = 0x0000] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0x00 0x00 getvar:version [lost] | |
| 0x03 0x00 0x00 0x00 getvar:version [lost] | |
| 0x03 0x00 0x00 0x00 getvar:version | |
| 0x03 0x00 0x00 0x00 | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x00 0x00 0x01 OKAY0.4 | |
| ---------------------------------------------------------------------- | |
| [Client packet loss and retransmission, S = 0x0000] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0x00 0x00 getvar:version | |
| 0x03 0x00 0x00 0x00 [lost] | |
| 0x03 0x00 0x00 0x00 getvar:version | |
| 0x03 0x00 0x00 0x00 [lost] | |
| 0x03 0x00 0x00 0x00 getvar:version | |
| 0x03 0x00 0x00 0x00 | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x00 0x00 0x01 OKAY0.4 | |
| ---------------------------------------------------------------------- | |
| [Host packet delayed, S = 0x0000] | |
| ID Flags SeqH SeqL Data ID Flags SeqH SeqL Data | |
| ---------------------------------------------------------------------- | |
| 0x03 0x00 0x00 0x00 getvar:version [delayed] | |
| 0x03 0x00 0x00 0x00 getvar:version | |
| 0x03 0x00 0x00 0x00 | |
| 0x03 0x00 0x00 0x01 | |
| 0x03 0x00 0x00 0x01 OKAY0.4 | |
| 0x03 0x00 0x00 0x00 getvar:version [arrives late with old seq#, is ignored] |